The present invention relates to management of data after being converted by an analog/digital conversion circuit, and particularly to an analog/digital conversion circuit of an in-vehicle semiconductor device for an automobile.
In recent years, CPUs and DSPs are provided at every part in an automobile, and data of various events (various data) generated in the automobile are sensed by the CPUs via sensors. The various data sensed by the CPUs and the like are fed back, and the CPUs provide functions. Further, when functions are provided by other CPUs and the like, the various data are transmitted to the other CPUs and the like via an in-vehicle communication network (for example, a LAN, a CAN (Control Area Network), an SCIF (Serial Communication Interface with FIFO), an I2C, and the like) to provide various functions in the automobile. A wide variety of examples of the functions include functions which are directly related to those of an automobile such as detection of torque generated by an engine and detection of the angle position of a steering wheel, functions necessary for securing safety required for a modern automobile such as an operation instruction to an air bag system, and functions for improving the comfort of a user such as control of an air conditioner and a GPS system, and control of a radio installed in the automobile.
In order to realize these functions, it is necessary to follow a series of procedures such as detection by a sensor, transmission to a CPU, determination of a controlled amount in the CPU, and execution of actual control. In the detection by a sensor, detected data are mostly analog data. A function of converting the analog data into digital data is performed by an analog/digital conversion circuit. The analog/digital conversion circuit samples and quantizes an analog signal output from the sensor to be converted into a digital signal. Such feedback control is periodically and continuously performed to catch up with changes in a system. A signal controlling process in which data after analog/digital conversion are referred to is started in a period of several tens of seconds to several hundreds of μ seconds in an automobile although it differs depending on functions.
In the analog/digital conversion circuit, an ADC is started in a single scan mode in a processing period shorter than the signal controlling process, and the converted digital data are buffered to a ring buffer in the order of conversion. Then, when the data of the ring buffer are used, the position of the latest data is calculated using the number of times of transfers of DMA, to refer to the data after the analog/digital conversion.